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Milestones are usually to be cheered, but not the one the world reached at 8 p.m. on Thursday, May 9. For the first time in millions of years the level of carbon dioxide in the Earth's atmosphere reached above 400 parts per million.

So what, you say? It's just a bunch of scientific numbers. Not really. What these numbers tell us is that within 25 years, if we continue to produce CO2 at our present rate, we can expect significant alterations in our climate.

Our seas will rise as the Earth heats up more in summer, melting the ice caps. Storms  both the summer and winter kinds  will get more extreme. As the amount of CO2 in oceans increases, more dead zones in offshore waters will spread.

What such changes will most affect, hands down, is the global economy. And one of the major economic casualties of rising sea levels and increasing temperatures will be Florida. Sure, 25 years from now the waves won't be lapping at Disney World's gates, but they will be washing away more of our wonderful, tourist-dollar-luring beaches. Coastal cities' drinking water supplies will suffer bigger salt-water intrusions, and residents in those cities will be in a gradual retreat from the encroaching tides.

This doesn't have to be the inevitable scenario. Not if Washington would stop its political infighting and finally start to listen to its own scientists. The National Oceanic and Atmospheric Administration announced the CO2 milestone after recording the numbers at its monitor on Mauna Loa in Hawaii last Thursday. NOAA has been tracking CO2 levels for more than 50 years there.

And the Scripps Institution of Oceanography in San Diego confirmed NOAA's findings, with its scientists issuing warnings that we are quickly losing the possibility of keeping the climate below what we consider "tolerable." (Later, NOAA adjusted its reading slightly to 399.89, but the Scripps Institute said its reading remained just above was 400.)

Bluntly put: Our window of opportunity for reducing CO2 and other greenhouse gas emissions is about to slam shut.

What a terrible legacy we will leave if Washington can't, very soon, find consensus on developing and making practical alternatives to the continued use of fossil fuels, particularly oil. There have been steps taken  in fits and starts  over the years. The Obama administration took a big one by increasing emission standards in vehicles.

But what else President Obama can initiate to curb greenhouse gases more in a Congress that can't, or simply won't, agree with him on much of anything is in doubt. The only thing that will force Congress' hand may be pressure  lots of it  from those who do listen to the government's scientists.

Topping that list should be Florida's leaders. The Sunshine State has so much to lose in the climate-change era. Gov. Scott, are you listening?